1. Field of the Invention
This invention relates to integrated circuit (IC) packaging technology, and more particularly, to a method of mounting a passive component, such as a resistor or a capacitor, over an IC package substrate, such as a BGA (Ball Grid Array) substrate
2. Description of Related Art
An IC package, such as BGA (Ball Grid Array, IC package, is designed to pack an IC device therein so that the IC device can be easily handled and mounted on a circuit board. In the package, the IC device is typically mounted together with some passive components, such as resistors and capacitors, on the substrate.
FIGS. 1A-1B are schematic sectional diagrams used to depict a conventional method of mounting a passive component over an IC package substrate. As shown in FIG. 1A, this IC package is a BGA type which includes a substrate 10, an IC chip 20, a passive component 30, a molded compound 40, and an array of solder balls 50. The IC package configuration of FIG. 1A is conventional and well-known to those skilled in the art of IC packaging, so description thereof will not be further detailed. FIG. 1B shows an enlarged view of the part enclosed in the dashed circle in FIG. 1A where the passive component 30 is mounted. As shown, the substrate 10 has a core portion 102 and a surface-mount portion 10b on which a pair of solder pads 11, 12 are provided; and the passive component 30 is mounted in such a manner that its two ends 31, 32 are electrically bonded by means of solder 12a respectively to the solder pads 11, 12.
One problem to the mounting of the passive component 30 over the substrate 10, however, is that a gap 13 would be undesirably left between the passive component 30 and the substrate 19. The existence of this gap 13 would abuse the following drawbacks during the manufacture of the IC package.
First, during the process for attaching the solder balls 50, the high-temperature condition would cause the solder on the passive component 30 to be partly melted, and the melted solder would then flow into the gap 13 through capillary effect, thus undesirably resulting in a bridged short-circuit between the two ends 31, 32 of the passive component 30. This bridged short-circuit may cause the internal circuitry of the IC chip 20 to be inoperable.
Second, during the compound-molding process, the gap 13 would cause the so-called popcorn effect when subjected to thermal stress, which would undesirably degrade the quality of the overall IC package configuration.
Third, during the compound-molding process, since the passive component 30 is fixed in position over the substrate 10 only by the solder applied to the two ends 31, 32 thereof, it can he easily forced out of position by the impact from the flowing resin used in the compound-molding process. If the impact is large, it can cause dismounting and even electrically disconnection of the passive component 30.
There exists therefore a need in the IC industry for a new method of mounting a passive component over an IC package substrate, which can help eliminate the above-mentioned drawbacks of the prior art.
It is therefore an objective of this invention to provide a method for mounting a passive component over an IC package substrate, which can help prevent the mounted passive component from being subjected bridged short-circuit.
It is another objective of this invention to provide a method for mounting a passive component over an IC package substrate, which can help prevent the overall IC package configuration from being subjected to popcorn effect.
It is still another objective of this invention to provide a method for mounting a passive component over an IC package substrate, which can help fix the mounted passive component more securely in position over the substrate.
It is yet another objective of this invention to provide a method for mounting a passive component over an IC package substrate, which can help allow the manufactured IC package to be more assured in quality and more reliable to use.
In accordance with the foregoing and other objectives, the invention proposes a new method for mounting a passive component over an IC package substrate. The method of the invention is characterized in the use of an electrically-insulative material, such as epoxy resin, to fill up the gap between the passive component and the substrate. The filling can be performed in two ways: either after or before the passive component is attached.
In the fist case (i.e., filling after the passive component is attached in position), the method of the invention comprises the following steps: (1) providing a pair of solder pads at predefined locations over the substrate; (2) soldering the passive component to the solder pads, with a gap being left between the passive component and the substrate, (3) applying a flowable and curable electrically-insulative material to the periphery of the passive component, and through capillary effect, the flowable and curable electrically-insulative material would fill into the gap between the passive component and the substrate; and (4) curing the filled electrically-insulative material into hardened state.
In the second case (i.e., filling before attaching the passive component), the method of the invention comprises the following steps: (1) providing a pair of solder pads at predefined locations over the substrate; (2) pasting an electrically-insulative material over the area between the paired solder pads to a predetermined thickness that would allows no gap to be left between the passive component and the substrate when the passive component is mounted over the substrate; and (3) soldering the passive component onto the paired solder pads.
Since the method of the invention allows no gap to be left between the passive component and the substrate, it can help eliminate the drawbacks of the prior art, including bridged short-circuit, popcorn effect, and dismounting of the passive component. The invention is therefore more advantageous to use than the prior art.